Endodontics is a field of dentistry concerned with the biology and pathology of the dental pulp and periapical tissues. Endodontic treatment employs a set of techniques, such as chemomechanical debridement, irrigation, drainage of hard and soft tissue, trephination, and antimicrobial therapy, with the goal of avoiding the extraction of a damaged, infected or diseased tooth.
Normal vital pulp is sterile, and the role of bacterial infection in the pathogenesis of pulpal and periapical disease is well established. Infected or necrotic pulpal tissue renders the pulp chamber and root canal a potential reservoir of bacteria, and disinfection of the tooth is one of the primary justifications for the chemomechanical aspects of root banal therapy. Recent data demonstrate a high incidence of root canal failure in necrotic teeth treated in a single visit, attributed to bacteria remaining in complex anatomical spaces such as accessory canals, fins, deltas and isthmuses (Sjorgen et al., Int. Endo. J., 30:297-306 (1997)). Other studies have reported the ability of bacteria to migrate into dentinal tubules and survive therein (Nagaoka et al., J. Endodon., 21:70-73 (1995)). It is speculated that the success rate of endodontic treatment could be 26% higher if the root canal is successfully disinfected prior to the final restoration (Sjorgen et al., Int. Endo. J., 30:297-306 (1997)).
Root canal infections are characterized as polymicrobial infections which tend to 10 be dominated by anaerobic bacteria. As a group, the common endodontic microbes associated with treatment failure include F. nucleatum, P. intermedia, P. micros, S. intermedius, P. endodontlis, P. gingivalis, P. melaminogenica, E. lentum, V. parvula, S. sanguis, P. buccae, P. oralis, and P. acnes. (Haapasalo, FEMS Immunol. and Medical Micro. 6:213-217 (1993) and Sundqvist, J. Endodon., 7:257-262 (1992)).
Post-operative periapical pain and interappointment flare-ups are also routinely attributed to the presence of bacteria, and/or their by-products, within the root canal. Typically, an initial bacterial infection triggers a host-mediated inflammatory response, the consequences of which underlie the flare-up patient's clinical symptoms. It has been reported that bacteria surviving instrumentation and irrigation proliferate rapidly in empty root canals (Bystrom and Sundqvist, Oral. Surg. Oral. Med. Oral Pathol., 55:307-312 (1983)), and there is a positive correlation between the number of bacteria present in a root canal and the incidence of inter-appointment flare-ups. The presence of black-pigmented, gram negative anaerobes in the root canal usually accompanies patient complaints of pain, swelling, and tenderness to percussion (Haapasalo, FEMS Immunol. and Medical Micro., 6:213-217 (1993)). Thus, the successful elimination of bacteria from root canals may lower the incidence of flare-ups.
Antibiotics have historically been used as an adjunct to endodontic treatment either by systemic or local administration. Currently, antibiotic treatment for root canal infections and exacerbations is limited to systemic administration. Thus, in light of the established correlations between the primary and secondary effects of bacterial presence and the incidence of both interappointment flare-ups and treatment failure, there is a clear need for an efficacious method of delivering and sustaining substantial concentrations of intracanal medicaments, particularly antibiotics.
During the 1950's a polyantibiotic paste (PBSC) was devised for use as an intracanal medicament (Grossman, L. I., J. Amer. Dent. Assoc., 43:265-278 (1951)). PBSC consisted of penicillin to target gram positive organisms, bacitracin for penicillin-resistant strains, streptomycin for gram negative organisms and caprylate sodium to target yeast, all suspended in a silicone vehicle. Although, clinical evaluation suggested that polyantibiotic paste conferred a therapeutic benefit (fewer treatments to achieve a negative culture) the composition was ineffective against anaerobic species (which are now appreciated as the dominant species responsible for treatment failure). In 1975 the Food and Drug Administration (FDA) banned PBSC for endodontic use primarily because of the risks of sensitization and allergic reactions attributed to the penicillin.
This underscores the importance of improving historical endodontic methodologies, particularly local delivery methods, in light of contemporary knowledge and technological advances.